1. Technical Field
The present invention generally relates to an energy absorber for a bumper assembly of a vehicle in the form of a one-piece tubular body obtained from bent and welded sheet metal and a method for the manufacture thereof.
2. Discussion of Related Art
Patent EP-1384536 describe an energy absorber comprising a sheet metal semi-finished item that is bent and/or folded to obtain a multi-chamber profile. Before being transformed into said multi-chamber profile, said sheet metal semi-finished item is subjected to transforming processes such as die-cutting and/or embossing/forming. Once the multi-chamber profile is obtained, the ends of said profile are joined together to form said chambers by means of welding, riveting and/or adhesive bonding. In one embodiment, this sheet is bent to obtain a double chamber profile, joining its ends by means of welding, so there must be two welding beads in said joint.
Energy absorbers of the type comprising two U-shaped parts facing one another with the branches overlapping and welded together, such as that described in U.S. Pat. No. 6,474,709, are known on the market. To manufacture these absorbers it is therefore necessary to manufacture two different parts and join them by means of welding in their two facing overlapping areas, which involves a more complicated and more expensive manufacturing process than in the case of the present invention.
Document EP-1762438 discloses a shock absorber for a motor vehicle comprising a tubular hollow body of metal which has a rectangular or square cross-section. The hollow body is open at both ends and is made from a flat metal blank obtained by stamping. The flat metal blank is formed to the polygonal hollow body by angle-bending at longitudinal edges running in the longitudinal direction thereof between each two adjacent side walls, and is closed in the longitudinal direction by a longitudinal welding seam. Longitudinal reinforcing ribs are provided in opposite side walls of the tubular hollow body which are formed in the metal blank during stamping process.
A drawback with the shock absorber of cited document EP-1762438 is that said longitudinal edges between adjacent side walls are straight and continuous, making thus difficult a controlled deformation of the tubular hollow body when subjected to forces in the longitudinal direction. On the other hand, the technique of angle-bending a flat metal blank obtained by stamping prevents the possibility of providing the tubular hollow body with transverse corrugations extending into rounded edges connecting adjacent side walls. Furthermore, the technique of angle-bending a flat metal blank is not appropriate when using very high or ultra high strength steel for the metal blank.